Semiconductor devices, such as metal oxide semiconductor field effect transistors (MOSFETs) or simply field effect transistors (FETs) or MOS transistors, are the core building block of a vast majority of electronic devices. A FET includes source and drain regions between which a current can flow through a channel under the influence of a bias applied to a gate electrode that overlies the channel. The channel typically includes crystalline material, such as monocrystalline silicon. To increase carrier mobility, strain can be introduced into the channel region of the semiconductor device. In practice, it is desirable to accurately and precisely fabricate such semiconductor devices with a predetermined strain profile to thereby achieve devices having their intended performance characteristics and/or to improve production yield. However, the hardware tools and production processes used to fabricate such devices may exhibit performance and/or process variations. As a result, semiconductor devices may be fabricated with strain profiles that deviate from their intended strain values, which in turn can lead to performance issues and/or reduced production yield. Therefore, it is desirable to evaluate strain levels of crystalline structures within semiconductor devices.
One technique for evaluating the strain profiles of crystalline structures is transmission electron microscopy (TEM) nano-beam diffraction (NBD). TEM NBD is a microscopy technique in which a beam of electrons is transmitted through a thin sample, with the electrons interacting with the sample as the electrons pass through so as to produce an electron diffraction pattern with reflections that correspond to the crystal lattice structure of the sample including the lattice spacing. The position of reflections from a strained crystal lattice structure, such as strained crystalline silicon, is shifted with respect to that from an unstrained crystal lattice structure, e.g., unstrained crystalline silicon. Therefore, strain can be calculated by measuring the change of center positions of the reflections. Unfortunately, it can be difficult to identify precise center positions of reflections due to asymmetrical intensity profiles of the reflections as a result of strong dynamical diffraction effects, which can negatively impact the accuracy of the strain measurement(s).
Accordingly, it is desirable to provide methods for evaluating strain of crystalline structures including more precisely identifying the center positions of reflections of an electron diffraction pattern. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.